Comment by foota

Am I missing something?

"This was the answer I needed! Rather than visiting all the live objects, I wanted to only visit the dead ones, and reference counting would let me do that.

So I added a way of maintaining a reference count for all the nodes in the doc. When we produce a new document, we decrement the reference count of the old root node (it will always be 0 afterwards). So we recursively decrement the ref count of its children, and so on. This gives me exactly what I wanted — a way to find all the nodes that were not reused, without having to visit most of the nodes in the doc."

I think there's a bit missing from the description here in the and so on, you would only recurse on a node when it's new refcount is zero, right (and the set of zero refcount nodes produced is exactly the set of dead nodes)?

Isn't this sort of just like having a dirty flag on nodes, and then replacing dirty nodes?